Reducing propane production in an alkylation process



United States Patent 3,272,888 REDlJCllNG PROPANE PRODUCTION IN ANALKYLATION PRO CESS Richard S. Logan and Thomas Hutson, Jr.,Bartlesville,

01:121., assignors to Phillips Petroleum Company, a corporation ofDelaware No Drawing. Filed Nov. 16, 1964, Ser. No. 411,572 4 Claims.(Cl. Zed-683.43)

This invention relates to an improved alkylation process. In anotheraspect, this invention relates to an improved alkylation process whereinthe production of propane in the alkylation zone is reduced to aminimum.

The catalytic alkylation of an olefin with an isoparafiin to formhigh-octane gasoline boiling range products is well known in the art. Ina conventional alkylation process, an olefin feed comprising propyleneand butylenes is passed with isobutane to an alkylation zone wherein theolefin and isobutane feeds are contacted with liquid hydrofluoric acid,said hydrofluoric acid acting as an alkylation catalyst. The alkylationzone hydrocarbon eifiuent is separated from the acid catalyst andfractionally separated with the isobutanes and lighter hydrocarbonfractions recycled to the alkylation zone.

The production of propane in the alkylation zone substantially decreasesthe efficiency of the alkylation process, representing a net consumptionof isoparaifin in an undesirable side reaction. As the isoparafiin ismore valuable than propane, it is economically desirable to minimizepropane production in the alkylation zone.

Accordingly, an object of our invention is to provide an improvedalkylation process. Another object of our invention is to provide animproved process wherein the production of propane in an alkylation zoneis reduced to a minimum. Other objects, advantages and features of ourinvention will be readily apparent to those skilled in the art from thefollowing description and the appended claims.

We have discovered that the production of propane in the alkylation zonecan be reduced to a minimum by introducing propane into the alkylationzone so as to maintain a concentration of propane in the hydrocarbonfeed to the alkylation zone in the range of 7-22 weight percent,preferably 11-18 weight percent.

The invention is applicable to an alkylation process wherein an olefinis contacted with an isoparaffin in the presence of an alkylatingcatalyst such as hydrofluoric acid, sulfuric acid, phosphoric acid, or ametal halide with a hydrogen halide promoter. The olefin employed in thealkylation process is selected from the group of olefins having 3-5carbon atoms per molecule or mixtures thereof, and the isoparaffin isselected from the group consisting of isobutane, isopentane, or mixturesthereof.

Conventional alkylation conditions are employed in the alkylation of theolefins with isoparaffins. For example, assuming that the olefin feedcomprises propylene and butylenes, the alkylating agent comprisesisobutane and the catalyst comprises hydrofluoric acid, the temperatureof the alkylation zone is preferably maintained in the range of betweenabout 85-105 F. with the pressure maintained within the alkylation zonesufiicient to maintain a liquid phase reaction. The volume ratio of acidto hydrocarbon maintained in the alkylation zone is preferably in therange from about 8:1 to 0.8: 1. Normally, the residence time in thealkylation zone is within the range of 0.25 to minutes.

The alkylation zone effluent mixture can be subjected to conventionalseparation steps to separate catalyst, product alkylate, propane, othernormal paraffins and isoparafiins thereof. Wherein acid catalyst isemployed in the alkylation zone, the alkylation zone efiluent mixture isconventionally passed to a separation zone wherein the acid phase isseparated from the hydrocarbon effluent mixture. A portion of theseparated hydrocarbon effluent can be passed to a depropanizingfractionation zone wherein the propane is separated therefrom. Theresidual hydrocarbon fraction from the depropanizing zone in combinationwith the remainder of the hydrocarbon efi'luent from the alkylation zonecan be passed to a second fractionation zone wherein a product alkylatefraction is separated from the hydrocarbon feed. An isoparaffin fractioncan be recycled from the second fractionation zone to the alkylationzone.

By maintaining the concentration of the propane in the hydrocarbon feedto the alkylation zone in the range of 7-22 weight percent, theproduction of synthetic propane during the alkylation reaction isreduced to a minimum. It is recognized that the introduction of propaneas feed into the alkylation zone reduces the quantity of olefin andisoparaifin feed to the alkylation zone. Accordingly, preferably thepropane concentration in the feed is maintained at or near the optimumvalue so as to permit the maximum isoparaffin and olefin feed to thealkylation zone while holding the production of propane in thealkylation zone to a minimum. We have discovered that the optimumeconomic concentration of propane in the hydrocarbon feed to theisomerization zone is about 14 weight percent with the economic optimumconcentration based on an evaluation of the hydrocarbon alkylation Zoneefiluent to determine the increased value of the olefin feed due to thealkylation reaction.

The following examples are presented to illustrate the objects andadvantages of the invention.

Example I In this example, propylene is alkylated with isobutane at analkylation reaction temperature of 60 F. employing variant amounts ofpropane in the hydrocarbon feed to the alkylation zone as illustratedbelow in Runs 1, 2 and 3 of Table I. Hydrofluoric acid was employed asthe alkylation catalyst. The operating conditions and yield data arepresented below m Table I.

TABLE I Run 1 Run 2 Run 3 Operating Conditions:

Reactor temperature, F 60 60 60 Reactor Pressure, p.s.i.g 200 205 200 IC/01efin, Vol. Ratio 11.3 10. 8 12.2 HF/HG, Vol. Ratio 3. 2 2.9 2. 9Propane in Hydrocarbon Reactor Feed,

Wt. Percent. 0. 28 1. 53 15.64 Duration of Test, Hours 0.67 0.75 0.75 HFAcid Data, Wt. Percent Total Acidity 92. 42 92. 95 91. 42 Water 0. 760.99 0. 64 Acid soluble oils O. 26 1. 68 2. 14 Inorganic Fluorides 0. 190.28 0.30 Yield Data:

Alkylate/Olefin, Vol. Ratio 1. 57 1. 54 1. 64 Isobutane Consumed/Olefin,Vol. Ratio 1. 25 1.18 1. 22 Synthetic Propane, Wt. Percent of Propylene22. 0 19. 9 10. 2 Alkylate Data:

Reid Vapor Pressure, p.s.i 5. 00 4.70 5. 80 API Gravity 67.6 69.5 70.1ASTM Dist, F 760 mm IBP 118 120 110 5%. 153 155 141 10%. 168 169 162 50%215 205 207 430 348 351 428 443 EP 455 495 502 Motor Octane No. (+3 ml.TEL) 100. 9 Research Octane N 0. (+3 ml. TEL 100.0 10D. 0

1 Debutanized alkylate.

Comparison of Runs 1, 2 and 3 of Table I clearly establishes that theproduction of synthetic propane in the alkylation zone was significantlyreduced when the concentration of propane in the hydrocarbon feed to the3 alkylation zone was increased to 15.64 weight percent (Run 3).

Example II In this example, a mixed olefin feed was alkylated withisobutane at an alkylation temperature of 80 F., employing variantamounts of propane in the hydrocarbon feed to the alkylation zone asillustrated below in Runs 4, 5 and 6 of Table III. Hydrofluoric acid wasemployed as the alkylation catalyst. The composition of the mixed olefinfeed, as determined by chromatographic analysis, employed in Runs 4, 5and 6, is illustrated below in Table II.

TABLE II Run 4 Run 5 Run 6 Ethane 0. 1 0. 1 0. 1 Propane. 14.1 14.4 14.G Propylene 15. 5 16. 16. 4 Isobutano 24. 9 24. 3 24. 3 n-Butane 16. 416. 3 l6. 1 Isolontylene and Enter 14.0 14. 0 13.9 Trans-butene-2 7. 87. 7 7. 6 Cis-butene-2 5. 8 5. 8 5. 7 Isopcntane 1. 0 1. O O. 93methy1butene-1 0.2 0. 2 0. 2 n-Pcntanc 0. 1 0. 1 0. 1 2-methylbntene-10. 1 0. 1 0. 1

Total 100. 0 100. 0 100. 0

The operating conditions and yield data for Runs 4, and 6 are presentedbelow in Table III.

TABLE III Run 4 Run 5 Run 6 Operating Conditions:

Time in Reactor, seconds. 35. 2 33. 9 34.0 Reactor Temperature, F 80 8080 IC4/Olefin, Vol. Ratio-.- 171 176 175 IIF/HC, Vol. Ratio 12. 5 12.612. 7 Propane in Hydrocarbon Reactor Feed,

Wt. Percent 2. 20 7.61 14. 56 Duration of Test, I-Iours 4.0 4. 4.0 HFAcid Data, Wt. P61191117! Total Aeidit 86. 91 90. 51 01. 45 Water 2. 662. 67 2. 48 Acid soluble 2. 29 0. 80 0. 43 Inorganic Fluorides..- 0. 650. 69 0. 48 Yield Data Alkylate/Olefin, Vol. Ratio 1. 74 1. 71 1. 69Isobutane Consumed/Olefin, Vol. Ratio. 1. 22 1. 21 1. 27 SyntheticPropane, Wt. Percent of Propylene 30. 8 15. 6 7. 9 Alkylate Data: 1

Reid Vapor Pressure, p.s.i 6.40 5. 05 5. 90 API Gravity 72.0 70. 9 71.0ASTM Dist. F, 760 mm.:

IBP 101 110 107 146 172 162 157 213 214 280 278 334 330 P 397 400 MotorOctane No. (+3 ml. TEL) 104. 4 103.8 Research Octane No. (+3 m1. TEL)103. 8 103. 4 103. 2

1 Dcbutanized alkylate.

Comparison of Runs 4, 5 and 6 of Table III clear-1y establishes that theproduction of synthetic propane in the alkylation zone was significantlyreduced when the concentration of propane in the hydrocarbon feed to thealkylation zone was increased to 14.56 weight percent (Run 6).

As will be evident to those skilled in the art, various modifications ofthis invention can be made, or followed, in the light of the foregoingdisclosure, without departing from the spirit or scope thereof.

We claim:

1. A process which comprises passing propylene to an alkylation zonecontaining an alkylation catalyst, passing isobutane to said alkylationzone, maintaining liquid phase alkylation conditions within saidalkylation zone, maintaining a concentration of propane in the range ofabout 14 to about 16 weight percent in the total hydrocarbon feed tosaid alkylation zone, and maintaining said propane in the liquid phasethroughout the alkylation reaction.

2. A process which comprises passing a mixed olefin feed to analkylation zone containing an alkylation catalyst, each of said olefinsin said mixed olefin feed having 3-5 carbon atoms per molecule, passingisobutane to said alkylation zone, maintaining alkylation conditionswithin said alkylation zone, introducing propane into said alkylationzone so as to maintain a concentration of propane in the totalhydrocarbon feed to said alkylation zone in the range of about 14 toabout 16 weight percent and maintaining said propane in said alkylationzone in the liquid phase throughout the alkylation reaction.

3. In an alkylation process which comprises passing an olefin having 3-5carbon atoms per molecule to an alkylation zone containing an alkylationcatalyst, passing an isopar-aflin selected from the group consisting ofisobutane and isopentane to said alkylation zone, and maintaining liquidphase alkylation conditions within said alkylation zone; the improvementwhich comprises introducing propane into said alkylation zone in therange of about 14 to about 16 weight percent of the hydrocarbon feed tosaid alkylation zone, and maintaining said propane in the liquid phasethroughout the alkylation reaction.

4. The process of claim 3 wherein the temperature of said alkylationzone is maintained in the range between about -105 F.

References Cited by the Examiner UNITED STATES PATENTS 2,881,235 4/1959VanPool 260683.48 2,967,208 1/1961 Clauson et al 260683.61 3,007,98311/1961 Clauson 260683.61 3,200,883 8/1965 Phillips 260683.48 3,204,0108/1965 VanPoOl 260683.48

DELBERT E. GANTZ, Primary Examiner.

R. H. SHUBERT, Assistant Examiner.

1. A PROCESS WHICH COMPRISES PASSING PROPYLENE TO AN ALKYLATION ZONECONTAINING AN ALKYLATION CATALYST, PASSING ISOBUTANE TO SAID ALKYLATIONZONE, MAINTAINING LIQUID PHASE ALKYLATION CONDITIONS WITHIN SAIDALKYLATION ZONE, MAINTAINING A CONCENTRATION OF PROPANE IN THE RANGE OFABOUT 14 TO ABOUT 16 WEIGHT PERCENT IN THE TOTAL HYDROCARBON FEED TOSAID ALKYLATION ZONE, AND MAINTAINING SAID PROPANE IN THE LIQUID PHASETHROUGHOUT THE ALKYLATION REACTION.